The present invention relates generally to a system and method for guiding a beam of light through the orthogonal axes of a mechanical positioning system for directing the beam at an object for ultrasonic testing, and more particularly, to a system and method for delivering a laser beam generated by a remote laser source through a gantry positioning system for use in detecting material defects of a test object using ultrasonic techniques.
It is desirable for a variety of applications to provide for mechanically directing a laser beam to any location within a predetermined volume. Many of these applications are tailored specifically for use within industrial manufacturing applications employing automated, robotics systems. Over the past several decades, the advent of robotics and laser light source technologies have led to many integrated systems for assembly line manufacturing . For example, robotics assembly systems incorporating laser technologies are very typical in automobile and even aircraft manufacturing plants for performing such tasks as welding.
For many systems, a robotic or gantry positioning system having a mechanical armature is often used to direct a laser beam to a variety of locations of a single workpiece. This armature itself provides for precision directing of the laser beam from the end of the mechanical armature. A laser beam delivery system is normally integrated into the gantry positioning system (GPS), particularly into the mechanical armature, for directing the laser beam from the end of the mechanical armature to any location within a predetermined volume. Specifically, the laser beam is then directed to portions of a workpiece and often from various fields of view for welding, cutting, ablating, or any variety of applications employing a laser beam. While the concept of incorporating a laser beam delivery system into a mechanical armature system for delivering to a workpiece is known to those skilled in the art, the methods and manners for accomplishing this goal may be very diverse.
Various technologies employ a method or system for directing a laser beam through a robotics system, e.g. U.S. Pat. No. 4,661,680 xe2x80x9cEnd-of-arm tooling carousel apparatus for use with a robotxe2x80x9d by R. L. Swensrud; U.S. Pat. No. 4,659,902 xe2x80x9cRobot laser systemxe2x80x9d by R. L. Swensrud et al.; U.S. Pat. No. 4,539,462 xe2x80x9cRobotic laser beam, delivery apparatusxe2x80x9d by D. J. Plankenhorn. These technologies generally employ a plurality of tubular members, optically coupled to one another, through which a laser beam passes for directing the laser beam from the end of a GPS or xe2x80x9corthogonal axis manipulator systemxe2x80x9d (See Swensrud U.S. Pat. No. 4,659,902). These optical components for directing the laser beam through the laser beam delivery system may include spherical joint lenses or precision aligned mirrors at the pivotal connections of the armature of the GPS.
For GPSs that are relatively small in size and whose mechanical armature is light in weight, the directing of the laser beam through the armature may be provided by using a number of mirrors that are permanently located in fixed positions at the junctures of the mechanical armature. However, larger GPSs may include large carriage assemblies common to industrial workshops and other similar settings. The mechanical members of the GPS may bend and stress significantly depending on the position of the carriage assembly and the shape of the mechanical armature. These bends and stresses may result in laser beam steering within the segments of the GPS and ultimately may result in obstruction of the laser beam altogether. This stems from the fact that the mirrors are firmly attached to the mechanical armature of the GPS, and as the shape of the GPS bends, the mirrors: may come out of alignment. A common solution for this problem in those laser beam delivery systems that employ air cavity propagation of the laser beam in enclosed segments along the axes of the GPS is to require significantly large dimensioned enclosed segments to accommodate the substantial bending associated with a large GPS while maintaining a large working envelope. Additionally, larger mirrors may be required to accommodate and correct for this beam steering to ensure unobstructed transmission of the laser beam. This requirement may substantially increase the size of the laser beam delivery system within the GPS. This may also increase the cost for materials required for the laser beam delivery system as well as further complicate the integration of the laser beam delivery system into the GPS given its larger bulk.
Small GPSs may not suffer from such problems as severe bending and stresses given their relatively small size, yet the intrinsic different needs of various sized GPSs makes utilizing a single laser beam delivery system in variety of different sized GPSs extremely difficult. GPSs which are relatively small in size and light in weight do not require large members and mirrors through which a laser beam propagates; large GPSs require either a large working enveloped through which the laser beam travels or some additional modification to accommodate the bending of the mechanical armature of the GPS to maintain unobstructed laser beam propagation. However, some lasers suffer from beam pointing instabilities. This requires corrective alignment procedures to maintain long-term operation when employing long distance free space beam delivery methods. An approach for providing laser beam delivery through a gantry positioning system that is scaleable and adaptable to a variety of sizes and shapes of GPSs irrespective of the overall size and weight of the armatures of the GPS is desirable.
While a large GPS may comprise a laser beam delivery system with large members through which a laser beam propagates to overcome the problems of beam obstruction resulting from bending and stressing of the GPS as it changes shape, as described above, many problems remain in that the laser beam delivery system must be designed specifically for the GPS in question. The larger the size and heavier the weight of the GPS, the more beam steering may occur resulting in possible beam obstruction requiring larger members and mirrors to ensure unobstructed beam transmission. Such a solution to beam obstruction requires the size of the members through which a laser beam propagates be tailored specifically to the size, weight, and operating constraints of GPS in question.
Ultrasonic testing is a method which may be used to detect material defects in a objects comprised of various materials. A common application for ultrasonic testing is to detect inhomogeneities in composite materials. Ultrasonic testing may be used to serve a variety of industrial needs including identification of defects in manufactured goods for tuning of manufacturing processes. Manufacturers of products comprising composite material may wish to identify imperfections in their articles of manufacture to modify their manufacturing process to strive for greater repeatability and efficiency in their process or simply to identity problem areas within their process. Composite materials comprise many critical components within modern, high performance aircraft, and are becoming more common in terrestrial applications such as the automotive industry. Composite materials are desirable for many of their inherent attributes including light weight, high strength, and stiffness. Particularly for aircraft application, those composite material components, which may be large and complex in shape, are often flight critical necessitating strict assurance of material and structural integrity.
Unfortunately, these materials are sometimes fabricated with imperfections or develop them after several hours of use. These material defects may appear as a delamination of the surface of the material, porosity, an inclusion, debonds between bonded sub-components, or a void within the component itself. This inhomogeneity in the structure severely weakens it, providing a situation which might result in catastrophic failure. A conventional method for detecting material defects in a composite material utilizes piezoelectric transducers in conjunction with mechanical scanners mounted across the surface of the composite to detect any material imperfections. The disadvantages of the conventional methods are many, including difficulty in accommodating non-flat or evenly mildly contoured composite materials. Another disadvantage is the requirement that the transducer couple to the material via a water path. The transducer must remain normal to the surface within xc2x13xc2x0 during a scan. To accommodate highly-contoured and complex shaped components using conventional techniques often requires extremely time-intensive test set up preparation.
Laser ultrasonic testing is an alternative method that is used to identify these imperfections. For aircraft applications, particularly for military fighter aircraft, all flight critical parts fabricated of composite material must be fully inspected before installation. A GPS comprising a laser beam delivery system may be integrated with a laser ultrasonic testing system for providing automated identification of material defects of a test object.
One approach is to mount the laser ultrasonic testing system comprising a laser source on the end of the mechanical armature of the GPS. The use of a GPS allows the ultrasonic testing system to be maneuvered around the test object to provide for positioning the laser source in close proximity to the test object from a multitude of locations of fields of vision. For those ultrasonic testing systems which use high power gas lasers such as CO2 lasers, the large and bulky size of the laser complicates the integration of the ultrasonic testing system with the GPS as the end segment of the mechanical armature must be capable of supporting a significantly heavy weight at its end. The large size and bulky weight of the light source itself often demands the use of a very large GPS capable of supporting the heavy weight of an ultrasonic testing system as it is maneuvered around the test object to perform data acquisition from a variety of perspectives.
The conventional method of incorporating a GPS with an ultrasonic testing system cannot provide for the interfacing of data acquisition of the test object after the laser beam has been delivered to it from a remote location, aside from mounting the entire ultrasonic testing system on the end segment of the mechanical armature wherein only the laser source is located remotely. To overcome the requirement of a large and robust GPS to be used for ultrasonic testing of a test object for identifying material defects, a system or method is required which will not only provide for the delivery of a laser beam from a remote laser source, but also perform data acquisition of the test object from a remote location. Though the art provides for the combination of a GPS with a laser beam delivery system for the delivery of a laser beam to a workpiece, there is no teaching or suggestion for the integration of a GPS with an ultrasonic testing system which comprises a laser source and data acquisition system which is operated remotely from the workpiece as well as the end of the mechanical armature of the GPS.
The present invention utilizes a robotic or gantry positioning system (GPS) with an integral laser beam delivery system for delivering a laser beam from a remote laser source to a test object for detecting material defects using a laser ultrasonic testing system. The gantry positioning system may have the form of any variety of positioning systems commonly known to those skilled in the art. A typical configuration will generally include a mechanical armature that allows for the placement of its end to any location within a desired work space. This armature commonly includes a number of straight segments connected at each end and is operated using a number of actuators which provide for the moving and directing of the armature throughout the work space for some desirable or useful purpose. This GPS may take the form of a relatively small robotic-type armature; it may take the form of a system resembling an industrial crane common to machine shops and other industrial facilities; it may take the form of any number of configurations of various sizes and weights which provide for the movement of the end of a mechanical armature throughout the entirety of a defined work space.
The present invention includes a laser beam delivery system which is integrated into the GPS for transmitting a laser beam along the axes of motion of the GPS while its mechanical armature is in operation. The axes of motion of the GPS often correspond to the gantry members of the mechanical armature which combine to form the GPS; the gantry members are often connected in some pivotal manner to allow for freedom of movement in multiple directions. The laser beam is delivered through the entire GPS to a test object for performing ultrasonic testing on the test object. Each of the gantry members of the mechanical armature of the GPS comprises an optical transmission channel to guide the laser beam after being injected into the first gantry member of the GPS.
Additionally, the present invention provides a number of alignment fixtures within these optical transmission channels and a position feedback sensor to detect whether or not the laser beam is transmitting through the entire GPS free from obstruction. This position feedback sensor emits an alignment signal indicating whether or not the laser beam is transmitting fully through the alignment fixtures. The GPS allows the laser beam to be directed from the end segment of the mechanical armature at the test object from multiple points of view, thereby providing ultrasonic testing from all encompassing perspectives of the test object. For complete analysis of the test object, the GPS provides for ultrasonic testing of the object from a first field of view, then normally from several additional fields of view. Data from each of these fields of view is then utilized for detecting any material defects of the test object using ultrasonic techniques.
When using laser ultrasonic techniques, it is desirable to use a laser source of high output power to provide sufficient heat and excitation of the material of the test object. A typical laser source for use in ultrasonic testing is a carbon dioxide gas laser (CO2 gas laser). However, those skilled in the art will recognize a number of other lasers may also be used. A number of mirrors also assist to direct and guide the laser beam from the optical transmission channels of the various gantry members of the GPS. At least one mirror is located at the each of the connection points of the mechanical armature of the GPS to guide it from the optical transmission channels of adjacent gantry members. The angular alignment mirrors in the present invention is controlled by a number of mirror actuators which adjust the angular alignment of the mirrors in response to the alignment signals from the above-mentioned position feedback sensors. If the laser beam has somehow become obstructed and no longer transmits through the GPS, the mirror actuators change the angular alignment of the mirrors to re-align the path of the laser beam until transmission is re-established. Such a system and method provides for closed-loop error correction in real time to ensure transmission of the laser beam through the entire GPS.
Laser beam divergence is an additional problem that may occur in a system which provides for the directing of a laser beam, particularly where the medium of the system is air. For the present invention, a laser beam conditioning system comprises part of the laser beam delivery system for minimizing the divergence of the laser beam as it propagates through the GPS as well as providing for the conditioning of the beam to maintain certain properties after the laser beam has exited the GPS. Laser light diverges as it propagates due to its intrinsic Gaussian nature. Those skilled in the art recognize many different methods of minimizing the Gaussian beam divergence of a free space propagating laser beam.
A very common approach is to position a lens, or a sequence of lenses at predetermined locations along the propagation path of the laser beam to reshape the beam as it propagates to maintain the desired properties of the beam along the entire propagation path. For example, in the present invention, lenses could be placed along the optical transmission channels of the gantry segments at various locations that are calculated to maintain the same properties of the laser beam at entrance and exit of the GPS. The lenses may also be located near the mirrors which guide the laser beam from the optical transmission channels of the various gantry members of the GPS. Bulk optical lenses are not the only components of which the laser beam conditioning system provides may be comprised. Those skilled in the art can readily envision a number of additional components which may be used to minimize divergence of a propagating beam, such a various apertures, gratings, crystals, etc., which may all cooperate to minimize the divergence of the laser beam as it propagates through the GPS. Laser beam divergence may also present a problem after the laser beam has exited the end gantry member. The user of the present invention may wish to focus the laser beam on a specific location of the test object. A laser beam conditioning system provides the user with great flexibility to control various laser beam properties during transmission through the GPS as well as after the beam has left the GPS entirely.
The present invention employs a laser ultrasonic testing system which is used to identify and detect material defects in a test object. Data is acquired of the test object and is analyzed for identifying any material defects in the test object and for providing the precise locations of them. Identifying material defects in composite materials, particularly those within aircraft applications, may provide aircraft designers with information concerning actual life and fatigue of flight critical, composite components as well as provide manufacturers of composite components with information concerning stress and failure points of the component. The ultrasonic testing system within this invention is provided and presented in detail in U.S. patent application Ser. No. 09/343,920 entitled xe2x80x9cSystem and Method for Laser Ultrasonic Testingxe2x80x9d by T. E. Drake, Jr.
The present invention provides an important technical advantage by providing a laser beam delivery system which is scaleable and adaptable to a variety of gantry positioning systems (GPSs) of varying sizes and weight by providing closed-loop error correction of the transmission of a laser beam provided by a remote laser source through a GPS.
The present invention provides another technical advantage by providing for automated data acquisition of a test object by moving the end gantry member of a GPS around the test object in between various acquisitions of data thereby providing multiple fields of view of the test object for ultrasonic testing purposes.
The present invention provides another technical advantage by providing for focusing of the laser beam by using a laser beam conditioning system. This laser beam conditioning system permits the user of the present invention to control various properties of the laser beam that is used for ultrasonic testing purposes.